The invention relates to a wet-running direct-current motor for a fuel pump of an internal combustion engine of a motor vehicle.
German Patent DE 2531483 A1 discloses that severe brush wear can take place in these fuel pumps as a result of turbulence and the formation of a liquid wedge or cavitation between the brushes and the commutator of the motor.
It has therefore already been proposed that the commutator contact face be provided with a certain surface roughness, so that direct contact between the brushes and the commutator is preserved.
It has now been found, however, that fuel pumps with such construction are not suitable for pumping diesel fuel, especially biodiesel fuel, since they do not satisfy the useful life requirements of the motor vehicle manufacturers.
An object of the invention is therefore to provide means by which such a wet-running motor can be made suitable for use as a diesel fuel pump with a long useful life.
This object is achieved by the construction of a wet-running direct current motor for a fuel pump for an internal combustion engine, in which the commutator is formed from carbon lamellas and the brushes are made of carbon and the contact face of each brush is fluted or striated in the direction of rotation of the commutator.
It is a feature of the invention that the brush contact face is curved and has a radius whose center is offset in a direction counter to the direction of rotation of the commutator.
It is a further feature of the invention that the offset of the radius center is about 0.5 mm.
It is a further feature of the invention that the fluting of the brush contact face is formed by ribs disposed in parallel relation, the ribs having triangular cross-sections with apexes forming the brush contact surface.
It is a further feature of the invention that the apexes of the ribs have a spacing of about 0.5 mm from one another and the height of the apexes is about 0.2 mm.